Silent Hill (1 is best, but all are pretty scary)
Resident Evil 1 (rest weren't that scary)
AVP 1 or 2 (1 wasn't that much more scary then 2, AVP2 has better MP I also didn't like how getting acid on you pretty much kills you in #1)
Doom 3
FEAR
The Suffering was the most unfunny game... i woul dhave to say HALF LIFE is the scariest game... i played it when i was a young boy and it was crazy...
Might not be the scariest game but it was an amazing game. It had a very mature atmosphere, that's what I loved. It didn't have typical or childish dialogue.